As a rule the support tapes for a slide-fastener stringer are made of synthetic-fiber yarns, that is, yarns either wholly or principally made of synthetic-resin fibers. The use of this type of yarn is mandated by the requirement that the support tapes have virtually no elasticity, that is that they be virtually unstretchable so that the spacing between adjoining coupling heads of a coupling element secured to the edge of such a support tape will remain the same at all times. For this reason natural fibers such as wool are not used as these fibers are almost invariably elastic. Support tapes are generally formed of polyester or polyamide yarn which are subjected to a so-called thermofixing operation which shrinks and sets the yarns.
The disadvantage of such a slide-fastener stringer is that when used in a slide fastener and mounted in a garment it is obviously made of textile material which is often inconvenient in certain types of garments. In addition the tape is relatively hard so that when lying directly against the skin it can often be rather uncomfortable. Another difficulty lies in stitching the coupling elements to the edge of the tape, since the inevitably rather hard tape is rather difficult to sew.